1. Field of the Invention
The invention is in the field of box folding machinery.
2. Brief Description of the Background Art
In box folding machinery, particularly in the corrugated cardboard industry die cut box blanks arc fed into the folding section of a folder-gluer. The blanks are carried on a conveyor belt and the box sides are turned up by arms or belts for gluing to form the finished box. During the process glue is applied to an overlapping tab that is pressed onto the other box side as the folding is completed.
During this process, frictional forces produce a folding error known as "fish tailing" (See FIG. 1.) in which the upper panels at the glued seam, lag behind the lower panel that is being carried by the conveyor belt. Various methods have been devised to correct this folding error. For example, U.S. Pat. No. 4,547,183 discloses driving a set of upper belts, used to keep the folded box in compression while the glue sets, at a somewhat higher speed than the lower, conveyor belt in order to draw the upper panels forward. U.S. Pat. No. 5,217,425 makes similar use of upper drive wheels. However, adjustment of this system is critical and difficult to change from one box size to the next. With this method it is also difficult to stop driving the upper panels at the precise moment they are aligned with the lower panels.
In U.S. Pat. No. 4,976,672 gauge plates carried by an upper conveyor and moving in synchronism with the lower conveyor engage slots in both the leading and trailing edges of a folded box. This requires precise adjustment of the separation between the leading and trailing gauge plates for each box size.
In yet another prior art device, studs located below the lower conveyor are extended upward to intercept an approaching box being carried forward between the lower conveyor and an upper conveyor. The studs momentarily halt the forward progress of the box's lower panel, while the upper panel is urged forward by the upper belt, tending to square the box. While this approach has shown some promise, the prior art implementation has shown limited success. A reliable solution to the fish tailing problem is essential to the high-speed production of high quality boxes.